1. Field of the Invention
The present invention relates generally to a magnetic recording medium and more particularly to a tape-shaped magnetic recording medium including a backing layer, for executing recording/reproducing processes while being run at a high velocity.
2. Related Background Arts
In recent years, with a remarkable enhancement of information processing capability of a computer, a magnetic recording medium is increasingly required to have a much higher density and a much higher reliability. Therefore, for example, concerning a magnetic layer, there has been developed, as a layer suitable for a high-density record, a coated magnetic layer using a fine ferromagnetic metal powder having a specific area of 50 m.sup.2 /g or above and a coercive force of 1500 [Oe] or above, which layer has become available in recent years. The high-performance magnetic layer like this is expected to suit with the high-density record having a record wavelength of 0.5 .mu.m or under. Thus, even slight ruggedness or ununiformity on the surface of the magnetic layer of such a degree that there must be no problem in terms of utility when the record wavelength is large, might cause a decrease in output and/or an increase in noises, and then an occurrence of a drop-out. Hence, there have been made endeavors of drawing out the performance of the fine ferromagnetic metal powder to the utmost by obtaining more enhanced smoothness of the magnetic layer than ever before.
On the other hand, a size of the data to be dealt with becomes large, and a time necessary for the record and reproduction also increases corresponding thereto. It is also increasingly required to reduce this time. As one of approaches to this, it tends that a relative velocity between the magnetic head and the magnetic recording medium becomes higher and higher. In the case of the reproduction by a ring head, a reproduced output becomes larger as the relative velocity between the magnetic head and the magnetic recording medium increases, and hence the speed-up is desired in order to improve a magneto-electric transduction characteristic. With respect to a belt driven magnetic recording tape cartridge as disclosed in, e.g., U.S. Pat. No. 3,692,255, a product thereof is utilized, wherein the magnetic tape runs at a high speed, approximately 2 m/sec, between two tape reels.
When the tape is wound up at such a high speed, it might happen that the air is drawn between layers of the tape, resulting in slackened windings of the tape. In a worse case, a winding deviation might occur. There is known a technique for avoiding that deviation, wherein the windings are ensured by leaking the air drawn between the layers of the tape from gaps formed rugged portions on the surface of the backing layer, which surface is intentionally roughened.
Incidentally, the magnetic layer with its surface smoothed and the backing layer with its surface roughened, are adjacent to each other when the magnetic tape is wound. Thus, it might happen that a surface characteristic of the magnetic layer declines because of the ruggedness on the backing layer being transferred onto the surface of the magnetic layer. This phenomenon is called print-through. A problem of this print-through arises in the magnetic layer corresponding to a high record density using fine ferromagnetic metal powders. Besides, in the above-described belt driven magnetic record tape cartridge, the wound magnetic layer and the backing layer are pressed against each other by a strong force in which the pressing force due to a tension of the drive belt is added to a winding tension, and therefore the print-through in particular comes into the problem.
A reduction in the ruggedness on the backing layer is effective in avoiding the print-through but is undesirable because of worsening the running and winding characteristics. In this respect, there has been given so far no definite solution of how the surface of the backing layer usable for the high-density magnetic tape having a recording wavelength of, e.g., 0.5 .mu.m or under should be designed.